Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.28   8.320%   $225.6089   $225.61   $225.60   $225.60  
  Purchase #2 $91.41   9.127%   $99.753   $99.75   $99.75   $99.80  
  Purchase #3 $12.34   12.209%   $13.8466   $13.85   $13.85   $13.80  
  Purchase #4 $183.56   13.787%   $208.8674   $208.87   $208.85   $208.90  
  Purchase #5 $201.69   13.408%   $228.7326   $228.73   $228.75   $228.70  
  Purchase #6 $95.37   11.283%   $106.1306   $106.13   $106.15   $106.10  
  Purchase #7 $225.61   12.238%   $253.2202   $253.22   $253.20   $253.20  
  7 purchase totals = $1,018.26       $1,136.1593   $1,136.16   $1,136.15   $1,136.10